Sequence determinants on the NR2A and NR2B subunits of NMDA receptor responsible for specificity of phosphorylation by CaMKII

Abstract

Calcium/calmodulin-dependent protein kinase type II (CaMKII) and NMDA-type glutamate receptor (NMDAR) are neuronal proteins involved in learning and memory. CaMKII binds to the NR2B subunit of NMDAR in more than one mode, a stable association involving a noncatalytic site on CaMKII and an enzyme–substrate mode of interaction by its catalytic site. The latter binding results in phosphorylation of serine-1303 on NR2B. We have investigated this binding by studying the kinetics of phosphorylation of synthetic peptides harboring nested sequences of the phosphorylation site motif. We find that residues 1292–1297 of NR2B enhance the affinity of the catalytic site-mediated binding of CaMKII to the minimal phosphorylation site motif, 1298–1308 of NR2B, as evident from measurements of K m values for phosphorylation. However, CaMKII shows decreased affinity towards the closely related NR2A subunit due to an -Ile-Asn- motif present as a natural insertion in the analogous sequence on NR2A.